Interpretation of a Lichen Lower Limit on Streambanks

Abstract

The vertical zonation of vegetation on a streambank provides a record of the lrydrologic conditions existing at that location. Using data from nine USGS stream gauge stations, this study assessed the correspondence between the lower distribution limit of the lichen Xanthoria elegans and three stream discharge parameters: 1) peak flood discharge, 2) number of days submerged, and 3) date of exposure on receding of annual flooding. The lower limit did not correspond with mean peak flood discharge or number of days submerged. At stations where the lower limit occurred g reater than 40 cm above mean low water, the Xanthoria lower limit corresponded best with the stream level occurring in late-June and may document a minimum grmving season necessary for the establishment of Xanthoria. Ice may prevent the establishment of Xanthoria lmver than 40 cm above mean low water. The lower limit of lichen growth has been used to interpret the legal boundary of high water along streambanks. The lower limit of Xanthoria in this study did not correspond with mean peak discharge or mean period of submergence and so, would be a poor indicator of high water level.